From "Ritesh Mistry" To Subject st: Re: adjusted percentages and adjusted odds ratios Date Fri, 19 Sep 2003 21:04:05 -0700

```a 20% probability is equal to an odds of 1:4, while a 17% probability is an
odds of .85:4.

taking a ratio of the two odds you get 1/.85 which is an of about 1.176.  A
OR of 1.7 is actually not that big and doesn't translate into a large
difference in percentages.

hope this helps.

ritesh

----- Original Message -----
From: <Elizabeth.EBY@med.va.gov>
To: <statalist@hsphsun2.harvard.edu>
Sent: Friday, September 19, 2003 8:46 AM

> Hi-
> Could someone help me out with understanding the relatively small
difference
> in adjusted percentages (20% vs 17%) compared to a more robust adjusted
odds
> ration of 1.7?  The adjusted percentages are controlling for covariates,
and
> were obtained using the predict sequence.
>
> Thank you,
>
> Elizabeth Eby
> Research Health Science Specialist
> Ann Arbor VAMC
> 734-769-7100 X6248
>
> -----Original Message-----
> From: Copeland, Laurel
> Sent: Friday, September 19, 2003 11:28 AM
> To: Eby, Elizabeth
>
>
> I don't know. Maybe put the question to Statalist?
>
> -----Original Message-----
> From: Eby, Elizabeth
> Sent: Friday, September 19, 2003 11:27 AM
> To: Copeland, Laurel
>
> This hold even though those are adjusted percentages?
>
> -----Original Message-----
> From: Copeland, Laurel
> Sent: Friday, September 19, 2003 11:26 AM
> To: Eby, Elizabeth
> Cc: VHAANN HSRD Statistical Group
>
>
> The raw odds ratio can be calculated...17% of 334=277, 20% of 2741=2193
> cut back?
>     no  yes
> priv no   277  57
> ins? yes 2193 548
>
> OR = (277/57) / (2193/548)
>    =  4.86  /  4.00
>    = approx 1.22
> The remainder of the effect in the adjusted OR must be due to the
> covariates.
>
> -----Original Message-----
> From: Eby, Elizabeth
> Sent: Friday, September 19, 2003 11:05 AM
> To: VHAANN HSRD Statistical Group
>
> How would you explain the small difference in the adjusted percentages
(17%
> vs 20%) with an odds ratio of 1.7 (p=.04)?  Does it have anything to do
with
> the underlying sample sizes of the 2 groups (n=334 VA patients and n=2741
> with private insurance)?
>
> Thanks.
>
> -----Original Message-----
> From: jpiette@umich.edu [mailto:jpiette@umich.edu]
> Sent: Friday, September 19, 2003 10:51 AM
> To: elizabeth.eby@med.va.gov
> Subject:
>
> Liz - can you double check this?  THe difference in %'s seem small
relative
> to
> the AOR.
>
> Controlling for their sociodemographic characteristics, number of chronic
> diseases, and number of prescription medications, 17% of VA patients cut
> back
> on medication use due to cost compared to 20 % of those with private
> insurance
> (adjusted odds ratio [AOR]: 1.7, p=.04),
> *
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```